"Sweet Jesus? What the hell is this?"
Said of a liquid, more then naught coffee, that has been made so thick (or just became that way) and has so many noxious chemicals in it that drinking it is indeed an excercise in mortality. A spoon, when placed in the exact center of the glass, will stand straight up without help from you... at least, for a few seconds, until it dissolves in a mad hiss of smoke.
How to make an effective quanitity of brown gack? Take a pot of nasty drip coffee (no, not 'gourmet' coffee. Folgers from a Krupps). Let stand until half of the water content has evaporated. Add stuff. Any stuff. No-doz, wax, chocolate syrup, white-out and whatever else does it for you. Then go get a glass, preferably filled with a strong vodka because you're going to need a very stiff drink.
If it doesn't kill you, at least you'll go blind and loose all fine motor skills.